Having dominated the disc brake market in the late 2000s with the HFX, Hayes has been in the wilderness for a while. It’s spent several years data-logging braking habits and then developing the Dominion A4, and it’s paid off. This is a brake that performs well in real-world conditions, while being as user-friendly as possible.
The ‘clean sheet’ approach includes thicker-than-average rotors (1.95mm) and grub screws for micro-adjusting the position of the long four-piston caliper to ensure rub-free alignment.
Each brake is factory-tuned for minimum ‘dead stroke’, so the pad engagement is noticeably prompt and consistent. Reach is adjustable via a dial set into the lever blade and you can adjust the bite point with a 2mm Allen key.
Even with four big 17mm pistons, Hayes’ ‘LoFi’ (low lever force, high piston force) design and the fact that semi-metallic, rather than sintered, pads are fitted as standard mean that the braking is gently progressive, not grabby.
The bearing-mounted lever blades, solid handlebar connection and carefully-designed seals throughout mean that communication is very clean too, no matter how hard you’re pulling or how subtly you’re releasing the lever.
That makes the brake safe and sensitive to use in slippery conditions, which is great news now that we’re heading into the season of treacherous trails.
You can up the punch and bite with sintered pads, but as it stands you’ll definitely want to use 203mm rotors to boost power for gravity or e-bike use. At 489g (314g for the brake hose and caliper, 159g for a 180mm rotor and bolts, 16g for the mounting bracket) it’s heavier than SRAM’s Code RSC (487g), Magura’s MT7 (439g) and Shimano’s Saint (474g), which all feel more powerful on the trail.
Four big 17mm pistons and semi-metallic pads Mick Kirkman / Immediate Media
With bigger rotors, it’ll end up slightly heavier again. It’s the same weight as the less pokey Shimano XT four-piston unit though, and 40g lighter than TRP’s monster G-Spec Quadiem.
Hayes has included some neat details for everyday use. Rather than just having a single bleed port at either end for flushing bubbles out of the DOT 5.1 system, there are two built into the caliper (one for flushing out each side of the block).
This design worked really well when I needed to re-bleed the brake after installation. Also, the pad shape and the cut-outs in the ‘D-Series’ rotor have been designed to cancel out likely vibration frequencies and create a noise-cancelling effect, and they’ve certainly been quiet so far.
I can’t comment on wet-weather pad wear yet, but they’ve handled the heat of long descents fine. Having to remove the wheel to drop the pads out the bottom of the caliper is irritating though, and while the brake is certainly feature rich, that’s reflected in the high price.
Hayes Dominion A4 brakes specifications
Pistons: 17mm x 4
Pads: T106 Semi-Metallic
Rotor: D-Series (180, 203)
Reach adjust: Tool free
Pad contact adjust: Tooled
Lever pivot: Sealed cartridge bearings
Pad retention: King Pin
Bleed: 2-Stroke Dual Port Bleed System
Fluid: Hayes DOT 5.1
Graphics: Laser Etch